Capacitive structure

ABSTRACT

A capacitive structure, which structure is a length of a plurality of layers, each layer having opposed edges and comprising a dielectric substrate and a metallic film. The metallic film extends from one edge toward the other edge. Each layer includes a zone free of metallic film, which zone is spaced from the other edge and defines a narrow marginal metal film band at the other edge which is spaced from the remainder of the metallic film by the metal free zones. The layers are disposed with the metallic film of each layer being separated by dielectric material from the metallic film of the adjacent layer; the layers are offset such that first edges of a first group of layers lie outwardly beyond second edges of a second group of layers at one side of the structure, and first edges of the second group of layers lie outwardly beyond the second edge of the first group of layers at the other side of the structure, the layers of the first group alternating with the layers of the second group. The layers of each group are coated with electrically conductive material to electrically connect the metallic film of each layer of each respective group.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of U.S. patent applicationSer. No. 238,717, filed Feb. 27, 1981 and now abandoned.

This invention relates to layer or stack wound capacitors and to methodsand apparatus for making of the same.

One such method and apparatus is shown and described in U.S. Pat. No.3,670,378. In that patent the process for the production of thecapacitors comprises first forming capacitor bodies by winding alternatemetallic and dielectric films on a drum, contemporaneously windingseparating layers between the capacitor bodies to form a parent windinghaving alternate layers of capacitor bodies and separating layers, thenapplying a metallic spray coating to the edges of the parent winding toconnect metallic films, and thereafter severing the parent windingperpendicular to the separating layers to form the individual capacitorbodies. These resultant capacitor bodies have interwoven metallic layerswhich are separated by dielectric layers. The layers of one groupcomprising dielectric substrates and metallic films project outwardlyfrom one side of the capacitor body while another group of substratesand films project from the other side of the capacitor body. Themetallic coating is applied such that it connects electrically togetherthe metallic films on the outwardly projected group of layers. Thus,there are provided two electrodes or sets of capacitor "plates" whichare dielectrically isolated from one another but which are interwoven.

In the foregoing arrangement it sometimes happens that during thewinding process the being-wound layers will weave or depart from theirintended paths resulting in one or more layers being improperly locatedwith respect to the adjacent layers. If the separation between thegroups of layers is not sufficient, the capacitor may be short-circuitedor it may have a lower than intended dielectric strength at one or moreregions. If the separation is excessive the resulting capacitance of thecapacitor is reduced.

Moreover, although the foregoing arrangement provides economicalmanufacture of capacitors as compared with certain other manufacturingapproaches, such as wound capacitors, there is nevertheless a demand forfurther economies in capacitor manufacture. This demand for furthereconomies in capacitor manufacture is all the more immediate in view ofthe economic realities of the present-day capacitor marketplace wheresuch devices have almost come to be regarded as commodities so thatprice is often the single basis upon which buying decisions arepredicated. With such pressures existing with respect to selling price,the need to reduce cost of manufacture without degrading product qualityis particularly strong.

OBJECTS AND SUMMARY OF THE INVENTION

An object of this invention is to provide a high quality commercialcapacitor of the general type stated, but which is different instructure and wherein the manufacturing process is considerably lower incost.

A further object of this invention is to provide an arrangement of thetype stated which materially reduces the possibility of short-circuitingof the being-wound capacitor as a result of improper disposition of themetallic dielectric films.

Another object of this invention is to provide an arrangement of thetype stated in which the production of capacitors is much faster than ispossible with presently available equipment.

Another object of this invention is to provide apparatus of the typestated which functions to apply the layers forming the capacitor to adrum or transfer wheel directly from laminating or lay-on rollers. Suchan arrangement prevents the supply material from traveling unsupportedin space, thereby reducing weave and consequent misalignment of thecapacitor layers.

A further object of this invention is to provide an intermediate lengthof capacitive structure which is sufficiently rugged to withstand therigors of shipping to remote locations for further processing intoindividual capacitors.

In accordance with the foregoing objects the capacitor of the presentinvention comprises a plurality of layers having opposed edges, eachlayer comprising a dielectric substrate and a metallic film, themetallic film extending from one edge toward the other edge, each layerincluding a zone free of said metallic film, said zone being adjacent tobut spaced from said other edge to leave a narrow marginal film band atsaid other edge which is spaced by said zone from the remainder of saidmetallic film, said layers being disposed with the metal film of onelayer being separated by dielectric material from the metal film of theadjacent layer, said layers being offset such that at one side of thecapacitor said edges of a first group of layers lie outwardly beyondsaid other edges of a second group of layers, and at an opposite side ofthe capacitor said edges of the second group of layers lie outwardlybeyond said other edges of the first group of layers, the layers in thefirst group alternating with the layers of the second group and theoutwardly lying edges in each group being coated with electricallyconductive material to connect electrically the metal film layers ofeach group, said narrow marginal metallic film band thereby separatingthe adjacent coating material from the metal-free zone.

The method of this invention comprises providing first and second websof material each having a dielectric substrate, a metallic film coating,and narrow parallel longitudinal metal-free zones; slitting said websalong parallel lines that are offset from said metal-free zones to formribbons, each of which has a narrow marginal metal film band extendinginwardly from a longitudinal edge of the ribbon to said metal-free zone,winding said ribbons from said first and second webs alternately on adrum and in said winding offsetting the ribbons of one web from theribbons of the other web to form a plurality of adjacent interleavedrings of capacitance structure each having alternately disposed metaland dielectric layers and with there being in each structure the layersof the ribbons of each web respectively projecting laterally outwardlyfrom said marginal metal film band of the ribbons of the other web,coating the laterally projected parts of each structure with a metalsubstance to connect electrically the metal films of the respective websof the structure, and severing the structure transversely of the ribbonsto form capacitive ropes. The method of this invention further comprisessubjecting said capacitive ropes to pressure and heat to createsubstantially rigid, capacitive sticks and then separating saidcapacitive sticks into individual capacitors.

The apparatus of this invention comprises first and second supply rollsof webs, each web having a dielectric substrate with a metallic filmcoating, a rotatable drum spaced from said supply rolls, first andsecond laminator rollers, said rollers being circumferentially spacedwith respect to the periphery of said drum, a tension sensing rollerassociated with each laminator roller and in spaced parallel relationthereto to constitute with its associated laminator roller a rollerpair, one web being strained and tensioned over each roller pair, andmeans for slitting the web into ribbons prior to winding said ribbons onsaid drum to provide alternate layers of metallic and dielectricmaterial, said laminating rollers being sufficiently close to said drumand said slitting means being sufficiently close to said laminatingrollers such that the ribbons are supported over substantially theirfull length prior to winding onto said drum. Said roller pairs areoffset from one another such that, in winding said ribbons upon saiddrum, there are formed upon said drum a plurality of adjacentinterleaved rings of capacitance each having alternately disposed metaland dielectric layers and with there being in each structure the layersof the ribbons of each web respectively projecting laterally outwardlyfrom the edges of the ribbons of the other web.

The invention may also include the application to one of the webs of athin film of adhesive in at least a portion of the electric fieldregions of a capacitor, but the adhesive is not applied in the region ofslitting of the web or in the laterally projected parts of the structurewhere a spray contact is made with the metallic coating. The purpose ofthe adhesive is, to the extent needed, to lock the lamination so thatthe wound capacitor structure can be handled without delamination.

The invention may also include the application of heat to the ribbons asthey are wound upon the drum. Such application of heat should besufficiently frequent and sufficiently warm to tack adjacent layers ofribbons together as they are wound upon the drum so that the laminationis locked and the wound capacitor structure can be handled withoutdelamination.

In another aspect of the invention the webs can be passed through astation where a number of laser beams can burn off the metal to formprecisely spaced demetalized zones. These demetalized zones may be mademuch narrower by laser beam burn-off than would be obtainable bymaterial commercially available with conventional demetalized zones,which are much wider than is necessary for capacitors with low voltageratings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagrammatic view of apparatus constructed in accordancewith and for carrying out the method of the present invention;

FIG. 2 is a fragmentary sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a fragmentary top-plan view on an enlarged scale, of thestructure of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view taken along line 4--4of FIG. 3;

FIG. 5 is an enlarged diagrammatic view partially in section taken alongline 5--5 of FIG. 1;

FIG. 6 is a much enlarged fragmentary sectional view of parts of thecapacitor according to the invention;

FIG. 7 is an enlarged fragmentary portion of FIG. 2 and showingstructure for applying adhesive to the web; and

FIG. 8 is a diagrammatic showing of the laser burn-off station whichforms the demetalized zones as the web is withdrawn from its supplyroll.

DETAILED DESCRIPTION

Referring now in more detail to the drawing FIG. 1 there is shown a pairof supply rolls 2, 4 from which webs A and B are withdrawn. Each of thewebs A, B comprises a dielectric substrate 6 and a metallic film 8. Thesubstrate 6 may be of a suitable plastic such as the resin sold underthe trademark "Mylar". The film 8 may be a vapor deposited aluminum, andboth the substrate 6 and metallic film 8 are exceedingly thin. By way ofexample but not of limitation, the substrate 6 may be of the order of0.001 inches or less in thickness while the thickness of the metalizedfilm 8 may be of the order of 500 angstrom units. Each web A, B has aplurality of parallel demetalized or metal-free zones 10, as best seenin FIGS. 3 and 4 with respect to the web B. It is understod, however,that a like series of demetalized zones are provided on the web A. Thewebs A, B may have the demetalized zones 10 preformed thereon, or theymay be formed by a laser burn-off method as will later be described. Inany case the webs pass over a series of rollers respectively forslitting into ribbons and interleaved alternate winding onto a largediameter drum or transfer wheel 20.

In particular, the web A passes over an idler roll 12a, the axis ofrotation of which is shiftable to control weave of the web A. The idlerroll 12a moves in and out as a unit with the supply roll 2 under thecontrol of a conventional edge guide sensor (not shown) to control theweave. From the idler roll 12a, the web passes by the aforementionededge guide sensor to a tension sensing idler 14a. The tension sensingidler sends a signal to a variable drag clutch (not shown) on whichsupply roll 2 is mounted. This closed loop control maintains the tensionat any preset value. The apparatus also includes a laminating or lay-onroller 16a. Between the rollers 14a, 16a is a web-slitting station atwhich the web A is slit into a plurality of ribbons prior to passagearound the lay-on roller 16a and wrapping onto the drum or transferwheel 20. Similarly, the web B passes over a shifting idler 12b and fromthere to a tension sensing idler 14b past the slitting station onto thelaminating or lay-on roller 16b, where the idler 12b responds to asecond edge guide sensor (not shown) to control the weave of web B whilethe tension sensing idler 14b again sense a signal to a variable dragclutch (not shown) on which the supply roll 4 is mounted to maintain thetension at a preset value.

The slitting station for the web B comprises a plurality of spacedparallel cutters such as razor blades 21b which cooperate with apolished web support bar 22b over which the web B passes. Likewise, forthe web A the slitting comprises spaced parallel razor blades 21a (FIG.7) which cooperate with web support bar 22a. For each web the slittingstation forms a plurality of ribbons which immediately pass onto therollers 16a or 16b, as the case may be, and then onto the drum 20. Theresult is that the ribbons are supported substantially throughout theirfull lengths prior to winding onto drum 20. Because the ribbons do nottravel unsupported in space, weave is eliminated and the ribbons can beaccurately deposited onto the drum 20. This is in contrast to prior artarrangements which rely upon edge guides, sometimes unsatisfactorily, toprevent weave of the web.

The laminating or lay-on rollers press against the drum or transferwheel 20 and the razor blades may operate directly in narrow slits onthe rollers 16a, 16b. In any event, the arrangement for slitting thewebs provides smooth cuts by the razor blades without causing the webmaterial to wrinkle. This is particularly important as it is difficultto obtain smooth cuts without wrinkling in web material as thin as thatbeing utilized in the present invention. In the present apparatus, therollers 16a, 16b may be located either 90 degrees apart as shown in FIG.1, or 180 degrees apart.

The web B is slit into the plurality of ribbons 18b, as seen in FIGS.2-4. The web A is also slit to provide ribbons 18a which, like theribbons 18b, ultimately will become capacitor layers, as seen in FIG. 6.The slit lines for the web B are offset from the demetalized zones 10 soas to form marginal metal film bands 24 at one edge of each ribbon 18b.A like slitting takes place for the web A except, however, at the slitline for each blade 21a is offset from that as compared to FIG. 3 toform like marginal film bands 214 on the ribbons 18a. Thus, if the blade21b is located to the left of the demetalized zone 10 in cutting the webB (reference to FIG. 3) then for the web A the blade 21a will be to theright of the adjacent demetalized zone, as indicated by arrows 21aa inFIG. 3.

The ribbons are disposed simultaneously upon the drum 20 to produce thelayered pattern shown in FIG. 5. There are formed a plurality of hoopsor rings 30 of capacitor structure from which individual capacitors maybe formed. In FIG. 5 only one of the rings 30 is shown in cross-sectionfor purposes of clarity of illustration. Moreover, the sources of thevarious ribbons, namely from the supply web A or B, is indicated on oneof the structures 30 in FIG. 5. It will also be apparent that theribbons are not illustrated to scale, but rather are considerablyforeshortened. In any case, there is an initial winding of A layersadjacent to the drum 20, as shown by the lower five such layersdesignated in FIG. 5. Thereafter, the ribbons are interleaved and offsetfrom each other as they are simultaneously wound onto the drum 20 toform the pattern indicated by the A and B alternate layers in FIG. 5.Thereafter, another group of A layers are wound over the group of A andB alternate layers. The inner and outer A layers serve as reinforcementwhile the interweaved A and B layers or ribbons provide the activeportion of the capacitor structure.

Each of the separate rings 30 may be removed from the drum 20 and thesides 32, 34 thereof coated in a conventional manner with a metallicspray coating 40 (FIG. 6). The ring 30 may then be cut perpendicular tothe edges 32, 34 to form a length of capacitor structure. Thethus-formed length of capacitor structure is then subjected to pressureand heat to create a substantially rigid capacitive stick. Thatcapacitive stick can then be cut transversely to form individualcapacitor units.

FIG. 6 shows an enlarged sectional view through several inter-leavedlayers of the capacitor. It will be seen that at one side of thecapacitor metalized films 8a and the substrate 6a project laterallyoutwardly of the adjacent edges 36 of the layers 18b. The metalizedspray coating 40 electrically connects the metalized films 8a to form aset of capacitor electrodes or plates, this being made possible by thespace between the layers or ribbons 18a. The space between the left-handmetallic coating 40 of the top portion of FIG. 6 and the metalized layer8b of the ribbon 18b is at least the width of the metalized zone 10 plusthe width of the marginal metal film band 24. Thus, in effect, the band24 is a "floating" electrode. By providing for the floating electrodeformed by the band 24 the full width of the demetalized zone 10 isutilized for dielectric separation along the surfaces of the layers,thereby reducing the possibility of short-circuiting or changing thecapacitance of the capacitor from its prescribed value.

On the other side of the capacitor, as shown by the lower portion ofFIG. 6, the layers 18b project outwardly from the margin 37 of thelayers 18a for receiving the right-hand metal spray coating 40, shown inthe bottom portion of FIG. 6. The marginal metal film band 24 in thelower portion of FIGS. 6 and located on the layer 18a likewise serves asa "floating" electrode so that full advantage is taken of thedemetalized zones 10, as previously described.

In a modified form of the invention shown in FIG. 7 any suitable thinadhesive may be deposited on the web A by an applicator 50 positionedjust before the slitting operation occurs. Epoxy resin is one type ofadhesive that may be used, but the invention is not limited thereto. Theadhesive is not applied in the region of slitting or in the extensionareas of the web where the metallic spray is to be applied. The purposeof the adhesive, if needed, is to lock the lamination together afterbeing wound onto the drum 20 so that the structure 30 can be handledwithout delamination. The adhesive can be deposited and spread in a filmthickness substantially less than one micron, and the adhesive may thusbe used without materially reducing an efficient capacitance-to-volumeratio. An alternative or complementary approach to such locking of thelamination is by the application of heat to the ribbons as they arewound upon the drum. It is contemplated by this invention that suchapplication of heat would be sufficiently frequent and sufficiently warmto tack adjacent layers of ribbons together as they are wound upon thedrum.

The web material used in the present invention may be purchased with thedemetalized zones. However, these demetalized zones are usually somewhatlarger than is necessary for low voltage capacitors. Accordingly, asshown in FIG. 8, it is possible to form the demetalized zones 10 as theweb A or B is being withdrawn from the supply roll. This may beaccomplished by running the web through a laser burn-off station 52 atwhich laser beams 53 may be utilized to burn off the deposited metal andform an extremely narrow demetalized zone 10, much narrower than isprovided on commercially available webs. Consequently, material cost isreduced along with the size of the capacitor. The tension sensing andedge guide control systems employed in the present invention areavailable from Advanced Web Systems, Inc., 4793 Colt Rd., P.O. Box 6025,Rockford, Ill. 61125.

It is to be understood that, while the detailed drawings and specificexamples given describe the preferred embodiments of the invention, theyare for the purpose of illustration only, that the invention is notlimited to the precise details and conditions disclosed and that variouschanges may be made therein without departing from the spirit of theinvention which is defined by the following claims.

I claim:
 1. A capacitive structure comprising a length of a plurality oflayers, each said layer having opposed edges; each said layer comprisinga dielectric substrate and a metallic film, said metallic film extendingfrom a first one of said edges toward a second one of said edges, eachof said layers including a zone free of metallic film, said zone beingspaced from said second edge leaving a narrow marginal metal film bandat said second edge which is spaced by said zone from the remainder ofsaid metallic film, said layers being disposed with said metallic filmof each layer being separated by dielectric material from said metallicfilm of the adjacent layer, said layers being offset such that at afirst side of the capacitive structure said first edges of a first groupof layers lie outwardly beyond said second edges of a second group oflayers, and at a second side of the capacitive structure said firstedges of said second group of layers lie outwardly beyond said secondedges of said first group of layers, said layers of said first groupalternating with said layers of said second group, and the outwardlylying edges of said layers of each group being coated with electricallyconductive material to electrically connect said metallic film of eachlayer of each respective group.
 2. A capacitive structure as recited inclaim 1, wherein said capacitive structure further comprises electricalconnection means bonded to said electrically conductive material tofacilitate electrical connection of said capacitive structure inelectrical circuitry.
 3. A capacitive structure as recited in claim 2wherein said capacitive structure further comprises protectiveenveloping means applied to encapsulate said capacitive structure in amanner providing electrical insulation and moisture resistance for saidcapacitive structure while permitting electrical connection to saidelectrical connection means.
 4. A capacitor comprising a plurality oflayers, each of said layers comprising a dielectric substrate and ametallic film upon said substrate, said metallic film coveringsubstantially all of a first side of said substrate of each of saidlayers, said metallic film being interrupted by a metal-free zone, saidmetal-free zone extending substantially parallel to a first of twoopposing edges of said substrate and spaced therefrom thereby definingtwo metallized regions upon said substrate extending respectively fromsaid first edge and a second edge of said substrate to said metal-freezone; said layers being disposed in two groups, layers of a first groupof said two groups alternating with layers of a second group of said twogroups, said metallic film of each layer lying adjacent the substrate ofan adjacent layer, said two groups of layers being offset so that saidfirst edges of said first group of layers extends beyond said secondedges of said second group of layers and said first edges of said secondgroup of layers extend beyond said second edges of said first group oflayers, said extending first edges of said first and second groups oflayers being respectively coated with electrically conducting materialto electrically connect said metallized regions adjacent said firstedges of each group.
 5. A capacitor as claimed in claim 4 wherein saidcapacitor further comprises electrical connection means bonded to saidelectrically conductive material to facilitate electrical connection ofsaid capacitor in electrical circuitry.
 6. A capacitor as claimed inclaim 5 wherein said capacitor further comprises protective envelopingmeans applied to encapsulate said capacitor in a manner providingelectrical insulation and moisture resistance for said capacitor whilepermitting electrical connection to said electrical connection means. 7.A capacitive structure comprising a length of a plurality of generallyplanar layers extending from a first end to a second end, each saidlayer having a width extending from a first edge to a second edge; eachsaid layer comprising a dielectric film substrate and a metallic patternapplied to said substrate, said metallic pattern comprising a firstmetallic region extending from said first edge toward said second edgeto a first boundary substantially parallel to said second edge and asecond metallic region extending from said second edge toward said firstedge to a second boundary substantially parallel to said second edge;said first metallic region and said second metallic region extendingfrom said first end to said second end, said first boundary beingfurther displaced from said second edge than said second boundarythereby defining a metal-free zone intermediate said first boundary andsaid second boundary; said layers being disposed with said metallicpattern of each layer being separated by dielectric film substrate fromsaid metallic pattern of an adjacent layer, said layers being offsetsuch that at a first side of the capacitive structure said first edgesof a first group of layers lie outwardly beyond said second edges of asecond group of layers, and at a second side of the capacitive structuresaid first edges of said second group of layers lie outwardly beyondsaid second edges of said first group of layers, said layers of saidfirst group alternating with said layers of said second group; saidfirst group of layers thereby presenting said metallic region at saidfirst side of the capacitive structure and presenting said secondmetallic region at said second side of the capacitive structure, andsaid second group of layers thereby presenting said second metallicregion at said first side of the capacitive structure and presentingsaid first metallic region at said second side of the capacitivestructure; whereby, at each side of the capacitive structure, saidfirst, outwardly lying, edges may be electrically connected in common byelectrically conductive material and said second metallic regionselectrically insulate said second edges from said first edges andstructurally support the capacitive structure at said second edges.
 8. Acapacitive structure as recited in claim 7 wherein said capacitivestructure further comprises electrical connection means bonded to saidelectrically conductive material to facilitate electrical connection ofsaid capacitive structure in electrical circuitry.
 9. A capacitivestructure as recited in claim 8 wherein said capacitive structurefurther comprises protective enveloping means applied to encapsulatesaid capacitive structure in a manner providing electrical insulationand moisture resistance for said capacitive structure while permittingelectrical connection to said electrical connection means.
 10. Acapacitive structure as recited in claim 7 wherein said length is muchgreater than said width whereby said capacitive structure is a stick ofindiscriminate capacitance suitable for severing into segments ofdiscrete capacitance.
 11. A capacitive structure as recited in claim 7wherein said length is appropriate whereby said capacitive structure isa chip of discrete capacitance.